Demands for cellular downlink data are rapidly increasing as consumers use greater numbers of data intensive applications on their wireless data devices. This trend is encouraging wireless carriers and wireless service providers to explore new ways of increasing downlink data rates. One known method for increasing downlink data rates employs receive carrier aggregation. Receive carrier aggregation allows a wireless device to simultaneously receive data using multiple downlink frequency bands to improve throughput while simultaneously transmitting on another band. Receive carrier aggregation may be either contiguous or non-contiguous. In the case of non-contiguous carrier aggregation, receive carrier aggregation may be applied either intra-band or inter-band. The present disclosure relates to non-contiguous inter-band operation where a second receive band is located at a third harmonic of a transmit frequency.
In non-contiguous inter-band operation where one of the receive bands is located at the third harmonic of the transmit frequency, the harmonics generated in a power amplifier (PA) and front end (FE) switches are not attenuated sufficiently enough to prevent receiver desensitization. Related art methods for reducing receiver desensitization due to harmonics include improving a lower band duplex filter attenuation of the third harmonic of the TX frequency, improving the diplexer low band/high band (LB/HB) isolation, and adding continuously active (i.e., static) notch filters into the TX path, and the implementation of dual feed antennas with inherent LB/HB isolation.
However, these related art methods such as adding static notch filters into the TX path introduces insertion losses that significantly reduce efficiency. Reduced efficiency adversely impacts talk time and data transfer per battery charge of wireless devices. In addition, these related art methods may not significantly attenuate harmonics and distortion on an antenna side of an RF switch. Therefore, a need remains to either reduce the harmonic distortion in components making up the PA and the FE switches and/or include additional filtering in a low frequency transmit (TX) path to attenuate the generated harmonics without significantly impacting efficiency due to insertion losses. Moreover, a notch filter needs to be configured to attenuate harmonics and distortion that are self generated by switches coupled to the notch filter and other devices such as PAs, transceiver duplexers, and the like. Further still, the attenuation provided by a notch filter should prevent significant magnitudes of harmonics and distortion from reaching an antenna.